Generator assembly

ABSTRACT

An electric machine, such as a generator, providing for the generation of electricity and includes a rotor generating a magnetic field and a stator having stator windings. The interaction of the magnetic field with the stator windings generates current in the windings. The generator may provide the generated current to a power output of the generator, where it may be further transmitted to an electrical load to power the load.

BACKGROUND OF THE INVENTION

Electric machines, such as generators, provide for the generation ofelectricity from a mechanical force. The generation of the electricityoccurs due to the interaction of a rotating magnetic field in relationto a set of conductive windings. In one generator example, a rotorrotated by a mechanical force may generate the rotating magnetic fieldrelative to a stationary stator having a set of conductive windings. Theinteraction generates a current in the stator windings, which may beprovided to the power output of the generator, where it may be furthertransmitted to power an electrical load.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a generator assembly includes a stator having a core withmultiple poles, stator windings wound about the poles to define windingend turns at an end of the poles, a heat transfer element having a bodydefining a face confronting the end turns and comprising an aluminumalloy including a predetermined amount of Silicon Carbonate (SiC)providing the body with a first coefficient of thermal expansion, and athermally conductive, dielectric coating deposited on at least a portionof the face of the heat transfer element and in physical contact withthe stator windings, and having a second coefficient of thermalexpansion. The predetermined amount of SiC is selected such that thefirst and second coefficients of thermal expansion are close enough thatthe thermal expansion of the heat transfer element and the dielectriccoating in response to exposure to heat from the end turns will notresult in through cracking of the dielectric coating during normaloperation of the generator.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a sectional view of an electrical machine assembly.

FIG. 2 is a perspective view illustrating a stator of an electricmachine according to the first embodiment of the invention.

FIG. 3 is a partial sectional view taken along line III-III of FIG. 2showing a winding slot and slot liner according to the first embodimentof the invention.

FIG. 4 is an exploded view taken from a surface paralleling with andgoing through the axis of the stator, showing the stator assemblyaccording to the first embodiment of the invention.

FIG. 5 is an assembled view of the embodiment of FIG. 4.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention may be implemented in any environment using an electricmotor regardless of whether the electric motor provides a driving forceand/or generates electricity. For purposes of this description, such anelectric motor will be generally referred to as an electric machine,electric machine assembly, or similar language, which is meant to makeclear that one or more stator/rotor combinations may be included in themachine. While this description is primarily directed toward an electricmachine providing power generation, it is also applicable to an electricmachine providing a driving force and/or an electric machine providingboth a driving force and power generation. Further, the invention isapplicable in any environment using an electric machine.

FIG. 1 illustrates an electric machine assembly, such as a generator 1,comprising a first machine 2 having an exciter rotor 3 and an exciterstator 4, and a synchronous second machine 5 having a main machine rotor6 and a main machine stator 10. At least one power connection isprovided on the exterior of the generator 1 to provide for the transferof electrical power to and from the generator 1. Power is transmitted bythis power connection, shown as an electrical power cable 7, directly orindirectly, to the electrical load and may provide for a three phasewith a ground reference output from the generator 1.

The generator 1 further comprises a rotatable shaft 8 mechanicallycoupled to a source of axial rotation, which may be a gas turbineengine, about an axis of rotation 9. The rotatable shaft 8 is supportedby spaced bearings 11. The exciter rotor 3 and main machine rotor 6 aremounted to the rotatable shaft 8 for rotation relative to the stators 4,10, which are rotationally fixed within the generator 1. The stators 4,10 may be mounted to any suitable part of a housing portion of thegenerator 1. The rotatable shaft 8 is configured such that mechanicalforce from a running turbine engine provides rotation to the shaft 8.Alternatively, in the example of a starter/generator, rotation of therotatable shaft 8 of the generator 1 during a starting mode produces amechanical force that is transferred through the shaft 8 to providerotation to the turbine engine.

FIG. 2 illustrates the stator 10 in greater detail. The stator 10, asshown, comprises a generally cylindrical core 12, a plurality of posts14, at least one winding slot 16, and may optionally include at leastone slot liner 18 provided for at least some of the winding slots 16.The surface at the inner perimeter of the core 12 faces the rotor 6 andhas a plurality of spaced posts 14 defining a corresponding plurality ofspaced winding slots 16 therebetween, radially arranged at apredetermined spacing in the circumferential direction. Each of theplurality of winding slots 16 are configured with an open top facing thecircumferential center point of the core 12 and may terminate inopposing open ends spaced axially along the core 12. For instance, theends of the winding slot 16 may axially terminate at the same length asthe core 12. A slot liner 18 is placed along the inner perimeter of thewinding slot 16 defining an open top facing the circumferential centerpoint of the core 12 and terminating in opposing ends which are shownextending beyond the winding slot 16 open ends. Alternatively, the slotliner 18 terminating ends may not extend beyond the winding slot 16 openends. The core 12 may be formed from a plurality of laminations, butalternate forming or machining of materials is envisioned.

FIG. 3 illustrates a sectional view of a configuration of a singlewinding slot 16 assembled stator 10 having stator windings 20 accordingto one embodiment of the invention. The stator windings 20 compriseconductive wires (only a few are shown, not to scale, for illustrativepurposes) that are wound about the core 12 within the winding slot 16such that individual sets of windings 20 may be separated from othersets of windings 20 found in adjacent slots 16. Additionally shown, theslot liner 18 isolates the plurality of stator windings 20 from theplurality of posts 14 and the stator core 12. While only one set ofstator windings 20 are shown, it is envisioned that at least one set ofwindings 20 is wound around the axial ends of at least two posts 14(henceforth, “end turns”) and through at least two adjacent windingslots 16 such that the energization of the windings 20 form a magneticpole 22 at the intervening post 14. The rotation of a magnetic field atthe rotor 6 generates a corresponding voltage in the stator windings 20at the corresponding poles 22.

FIG. 4 illustrates an exploded view of the stator 10 of the generator 1taken from the longitudinal axis of the stator 10. As shown, the stator10 may further comprise a stator assembly 24 having a heat transferelement in physical contact with the stator 10 such that heat may betransferred from the core 12 to the stator assembly 24. In theillustrated example, the heat transfer element may comprise a first bodyelement 26 configured in a ring to encircle and receive the stator core12, and a second body element 28 also configured in a ring, andencircled and received by the first body element 26. Each of the firstand second body elements 26, 28 further define at least one abuttingface 30 configured to abut a respective axial terminating end 32 of thecore 12.

Each of the first and second body elements 26, 28 may comprise athermally conductive material, for example, an aluminum alloy having apredetermined amount of silicon carbonate (SiC) having a firstcoefficient of thermal expansion (CTE) according to the materialproperties. In one example, an aluminum alloy having a 30% reinforcementof SiC (by volume) may have a CTE of 14.0 ppm/° Celsius (° C.) betweenan operating temperature of 21-100° C. This example may further includea thermal conductivity of 165 Watts per meter-Kelvin at 21° C. While oneexample of an aluminum alloy having a 30% SiC is provided, alternativeheat transfer elements, such as aluminum alloys having differentpredetermined amounts of SiC, are envisioned.

The stator assembly 24 is configured such that the first body element26, stator core 12, and second body element 28 may be fixedly orremovably assembled, for example, by axially aligning each component 26,12, 28 along a common axis 34, and inserting the core 12 into the firstbody element 26, followed by inserting the second body element 28 intothe first body element 26, such that the abutting face 30 of each firstand second body elements 26, 28 abuts the core ends 32 of the core 12.

FIG. 5 illustrates a cross-sectional view of an assembled statorassembly 24. As shown, the stator assembly 24 may further comprise athermally conductive, dielectric coating 36 deposited on at least aportion of a face of the first and/or second body elements 26, 28. Thecoating 36 may be applied prior to or after assembling the statorassembly 24. Additionally shown are at least a portion of the statorwindings 20 end turns 38 axially extending outside the core 12 and slotliner 18 as they wind about the poles 22. It is envisioned that thestator windings 20 and/or end turns 38 are in physical and/or thermalcontact with the first and/or second body elements 26, 28, via thecoating 36, such that the elements 26, 28 and coating 36 provide heattransfer between the materials and/or layers. Additionally, thedielectric properties of the coating 36 electrically isolate the statorwindings 20 from the stator core 12 and the first and/or second bodyelements 26, 28.

The coating 36 may be adhered or deposited on to the first and secondbody elements 26, 28 through a number of techniques, for example, byincluding adhesives, plasma coating, or spray-on coating. Additionalcoating 36 adhesion or depositing techniques are envisioned. One exampleof the coating 36 may include a ceramics-based material, such asaluminum oxide, which has a second CTE, such as 6.3 ppm/° C. between21-100° C., however alternative conductive, dielectric materials orcoatings are envisioned.

During operation of the generator 1, the interaction of the rotatingmagnetic field with the stator windings 20 of the stator assembly 24generates a current through the windings 20, which may ultimately bedelivered to a generator output or electrical load for operating theload. The current generated in the stator windings 20 generates heat inthe windings 20, for example, at the end turns 38. The physical and/orthermal contact between the stator windings 20 and/or end turns 38, thecoating 36, and the body elements 26, 28 allows the heat generated inthe windings 20 to be thermally conducted through the coating 36 to thebody elements 26, 28, where it may be further dissipated, for example,via heat fins, air cooling, or through coolant traversing through acoolant passage in physical and/or thermal contact with the bodyelements 26, 28. Additional cooling techniques are envisioned.

It is envisioned that the predetermined amount of the SiC of thealuminum alloy is selected such that the first and second coefficientsof thermal expansion are close enough that the difference between thethermal expansion of the body elements 26, 28 and the coating 36 willnot result in through-cracking of the coating 36 in response to exposureto the heat generated by the end turns 38 of the stator windings 20during normal operation of the generator 1. Stated another way, therelationship of the SiC of the aluminum alloy is selected so that thethermal expansion of the aluminum alloy is more aligned to the thermalexpansion of the coating 36 so that the coating 36 does not crack duringthermal expansion. For example, the CTE of the body elements 26, 28 maybe higher or lower than the CTE of the coating 36. In the exampleprovided above, the first and second CTE may be within 7.7 units of eachother, however any first and second CTE within 10 units of each otherare envisioned. In this example, the difference between the first andsecond CTE is within 55 percent of the first CTE. The descriptionsprovided are non-limiting examples of possible relationships between theCTE of the body elements 26, 28 and the coating 36, and other relationalpercentages and/or relational coefficient limits are envisions.

Many other possible embodiments and configurations in addition to thatshown in the above figures are contemplated by the present disclosure.For example, one embodiment of the invention contemplates a heattransfer element having additional or fewer body elements configured toabut the stator core 12. Another embodiment envisions configuring thecoating 36 on alternative heat transfer element faces, yet still inphysical and/or thermal contact with the stator windings 20 or end turns38. Additionally, the design and placement of the various components maybe rearranged such that a number of different in-line configurationscould be realized.

The embodiments disclosed herein provide a generator assembly withimproved heat dissipation at the stator winding end turns. One advantagethat may be realized in the above embodiments is that the abovedescribed embodiments have superior thermal and electrical operationover the conventional generator configurations. With the proposedconfigurations, a high thermal conductivity between the end turns of thestator windings and the heat transfer element can be achieved due to thehigh thermal conductivity of the heat transfer element and the coatingas described above. The higher thermal conductivity allows for agenerator that can dissipate higher levels of heat. Since the amount ofheat generated in the stator windings is related to the amount ofelectricity generated, the above-described embodiments allows for anelectric machine capable of generating more power than conventionalmachines.

Additionally, the dielectric strength of the coating layer reduces oreliminates the likelihood of an electrical short between the statorwindings and heat transfer element, even at higher current and voltagegeneration by the electric machine. The combination of higher thermalconductivity and dielectric strength of the embodiments described hereinresult in a stator assembly which can be used in higher thermal classapplications due the improved ability to dissipate heat away from thestator windings. Thus, another advantage of the above describedembodiments is that electric machines having the described generatorassembly may be driven to generate more power and at higher temperaturesthan the conventional electric machines.

Furthermore, by providing the heat transfer element with a predeterminedamount of silicon carbide, the generator assembly may be configured toprovide a closer matching coefficient of thermal expansion between theheat transfer element and the coating. Thus, when the heat transferelement and the coating are heated during the heat dissipation, they maybe configured to expand at a similar or closer rate, reducing the likelyhood that a disparity in expansion rate may crack the coating. Byreducing the likelihood of developing cracks in the coating, thelikelihood of developing electrical shorts between the stator windingsand the heat transfer element is reduced as well.

In even yet another advantage of the above-described embodiments is thatby providing improved heat dissipation of the stator windings, and thusallowing the windings to operate at a lower temperature, as well asincluding a coating material such as ceramic, which may require lessmaintenance and a higher mean time between failures, the overalloperating life of the generator is improved, and/or the maintenance timeand costs of the generator are reduced. When designing electric machinesystems, an important factor to address is reliability. Improvedoperating life, and reduced maintenance time and costs result incompetitive advantages.

To the extent not already described, the different features andstructures of the various embodiments may be used in combination witheach other as desired. That one feature may not be illustrated in all ofthe embodiments is not meant to be construed that it may not be, but isdone for brevity of description. Thus, the various features of thedifferent embodiments may be mixed and matched as desired to form newembodiments, whether or not the new embodiments are expressly described.All combinations or permutations of features described herein arecovered by this disclosure.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A generator assembly comprising: a stator havinga core with multiple poles; stator windings wound about the poles todefine winding end turns at an end of the poles; a heat transfer elementhaving a body defining a face confronting the end turns and comprisingan aluminum alloy including a predetermined amount of Silicon Carbonate(SiC) providing the body with a first coefficient of thermal expansion;and a thermally conductive, dielectric coating deposited on at least aportion of the face of the heat transfer element and in physical contactwith the stator windings, and having a second coefficient of thermalexpansion; wherein the predetermined amount of SiC is selected such thatthe first and second coefficients of thermal expansion are close enoughthat the thermal expansion of the heat transfer element and thedielectric coating in response to exposure to heat from the end turnswill not result in through-cracking of the dielectric coating duringnormal operation of the generator.
 2. The generator assembly of claim 1wherein a difference between first and second coefficients of thermalexpansion is within 55 percent of the first coefficient of thermalexpansion.
 3. The generator assembly of claim 1 wherein the first andsecond coefficients of thermal expansion are within 10 units of eachother.
 4. The generator assembly of claim 1 wherein the firstcoefficient of thermal expansion is 14.0 ppm/° Celsius (C) and thesecond coefficient of thermal expansion is 6.3 ppm/° C.
 5. The generatorassembly of claim 1 wherein the temperature of the end turns duringnormal operation is between 200 and 280 degrees C.
 6. The generatorassembly of claim 5 wherein the generator generates at least 120kilowatts during normal operation.
 7. The generator assembly of claim 4wherein the amperage of the current through the windings during normaloperation is 67 amps.
 8. The generator assembly of claim 1 wherein thepredetermined amount of SiC is at least 30%, by volume.
 9. The generatorassembly of claim 1 wherein the thermally conductive coating is a plasmacoating.
 10. The generator assembly of claim 1 wherein the thermallyconductive coating is a spray-on coating.
 11. The generator assembly ofclaim 1 wherein the body further comprises a coolant passage such thatcoolant traversing through the coolant passage cools the body.
 12. Thegenerator assembly of claim 1 wherein the dielectric coating comprises aceramic.
 13. The generator assembly of claim 12 wherein the ceramiccomprises aluminum oxide.
 14. The generator assembly of claim 12 whereinthe ceramic has a coefficient of thermal expansion of 6.3 ppm/° C.